A problem that is encountered in finished paper is its high tendency for dust formation, the reason for which are fiber particles and filler particles released from the paper surface. The dust gives rise to problems already at the drying stage in paper making, but above all in the machines and equipments handling paper, such as in printing equipment. The printing methods as such are developed which means high machine speeds and long printing series. High speeds aggravate dust formation, and long printing series reduce standing times, during which it would be possible to carry out a cleaning of the equipments.
In order to solve the dusting problem it is known to use methods, which is a rule are based on chemical compounds to be added to the fiber pulp, prior to the paper web formation. The use of mineral and micro waxes, of sizing agents, such as AKD and ASA dispersions, of wet strength resins and of pulp sizing starch is known. Irrespective of these known measures, paper dusting is still a significant problem.
Low strength between long fibres, short fibres and fines and fillers give rise to increased dust formation. The number of contact points between fibres, fines, fillers and dry strength aid e.g. wet end starch impact on strength properties. A large number of the contact points, into which starch or other dry strength aid is adsorbed in between, leads to good strength properties. In cases where the quantity of short fibres, fines and fillers is high and the amount of long fibres is thus correspondingly low, conventional non-degraded cationic starches do not increase strength in a satisfactory way. One possible explanation is that the molecular weight of starch is too big to reach in a sufficient quantity to the contact points or the quantity of the molecules is just too little and the result is thus poor strength.
Fiber lengths of fibrous material, which is used on paper making are typically between 0.05–4 mm. The fractionation of fibrous material can be done by several means e.g. by Bauer-McNett or by Clark classifier. The classification of fibres in pulp is described e.g. in Tappi Test Method T 233 cm-95. The term long fibres mean in this application those fibres with the fiber length 1.68 mm or greater. Fibres longer than 1.68 mm mean those fibres, which retain on Tyler screen 10 according to Tappi Test Method T 233 cm-95, in the case that the length of the fibres can't be determined otherwise. The term fibres means in this application long fibres, short fibres and fine material, which is based on fibrous material. Fillers are thus excluded in the term fibres.